A method of producing a piston rod by joining end surfaces of a rod main body and a rod head to each other by a friction welding is known. JP2011-56531A discloses a technique to join, by the friction welding, a rod main body whose axial-center portion of an end surface is recessed and a rod head whose axial-center portion of an end surface is recessed in a similar manner. With this technique, because it is possible to reduce the joining area compared with a case in which the end surfaces are not recessed, a size of an equipment for the friction welding can be reduced.